Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing a first image in a sequence according to the claimed design;

FIG. 2 is a front view showing a second image in the sequence; and,

FIG. 3 is a front view showing a third image in the sequence.

The appearance of the image transitions sequentially between the images shown in FIGS. 1 through 3. The process or period in which one image transitions to another image forms no part of the claimed design.

The shading depicts a contrast in appearance.

The outermost long-dash broken lines illustrate an electronic device, which is the environment of the design, and form no part of the claim. The remaining broken lines illustrate portions of the display screen and portions of the graphical user interface that form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 